Section 1 The Theory of Evolution Focus by Natural · PDF file · 2011-08-18Darwin’s theory of evolution by ... Section 1 276 Chapter 13 • The Theory of Evolution Pg. 276: 3A,

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This lesson describesDarwin’s experiences as a natural-ist, how his curiosity about thethings he saw prompted him toconclude that evolution occurs, andhow he developed an explanationfor the mechanism of evolution.Students will also learn howDarwin’s theory of evolution bynatural selection has been modifiedby other scientists with regard toformation of new species.

Write the following headings on theboard: Long life span; Short lifespan. Have students write a fewsentences in which they relate anorganism’s life span to the potentialrate of evolution of a species.(Species with shorter life spans canpotentially undergo evolutionarychange much faster than species withlonger life spans.)

DemonstrationShow students pictures of severaldifferent varieties (breeds) of a com-mercially important plant or animal.Ask students how these varietiesoriginated. (All originated throughselective breeding by humans.) If pos-sible, show students pictures of thewild ancestors of the organisms. Tellstudents that observations of changein domesticated animals and plantshelped people recognize that speciescan change over time. TAKS 3 Bio 7A

(grade 11 only)

MotivateMotivate

Bellringer

FocusFocus

Section 1

276 Chapter 13 • The Theory of Evolution

Pg. 276: 3A, 3C, 3E, 3F, 7B

• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Quick Lab GENERAL

GENERAL

GENERAL

Chapter Resource File Transparencies

TT BellringerTT Darwin’s FinchesTT Two Rates of Progression

• Reading Organizers• Reading Strategies

Planner CD-ROM

Darwin Proposed a Mechanism for EvolutionThe idea that life evolves may have been first proposed by Lucretius,a Roman philosopher who lived nearly 2,000 years ago before themodern theory of evolution was proposed. Then, in 1859, the Eng-lish naturalist Charles Darwin, shown in Figure 1, published con-vincing evidence that species evolve, and he proposed a reasonablemechanism explaining how evolution occurs.

Like all scientific theories, the theory of evolution has developedthrough decades of scientific observation and experimentation. Themodern theory of evolution began to take shape as a result of Dar-win’s work. Today almost all scientists accept that evolution is thebasis for the diversity of life on Earth.

As a youth, Darwin struggled in school. His father was a wealthydoctor who wanted him to become either a doctor or a minister.Not interested in the subjects his father urged him to study, Darwinfrequently spent more time outdoors than in class. At the age of 16,Darwin was sent to Edinburgh, Scotland, to study medicine.Repelled by surgery, which at the time was done without anesthet-ics, Darwin repeatedly skipped lectures to collect biological speci-mens. In 1827, Darwin’s father sent him to Cambridge University, inEngland, to become a minister. Although he completed a degree intheology, Darwin spent much of his time with friends who were alsointerested in natural science.

In 1831, one of Darwin’sprofessors at Cambridge rec-ommended him for a positionas a naturalist on a voyage ofHMS Beagle. Although theship had an official natural-ist, the Beagle’s captain pre-ferred to have someoneaboard who was of his ownsocial class. At the age of 22,Darwin set off on a journeythat would both change hislife and forever change howwe think of ourselves. Theship and its route are shownin Figure 2.

Section 1 The Theory of Evolutionby Natural Selection

Objectives● Identify several observations

that led Darwin to concludethat species evolve.

● Relate the process of naturalselection to its outcome.

● Summarize the main points of Darwin’s theory of evolution by natural selection as it is stated today.

● Contrast the gradualism and punctuated equilibriummodels of evolution.

Key Terms

populationnatural selectionadaptationreproductive isolation gradualismpunctuatedequilibrium

Figure 1 Charles Darwin.Darwin was born in England in1809 and died in 1882.

3C 3F

7B

3A

3E

276

Student Edition TAKS Obj 1 IPC 3ATAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B TEKS Bio 3A 7A, 7B; IPC 3A

Teacher Edition TAKS Obj 1 Bio/IPC 1A, 2A TAKS Obj 1 IPC 3A TAKS Obj 3 Bio 7A TEKS Bio 3A, 3F, 7A; Bio/IPC 1A,2A; IPC 3A

pp. 276–277

TAKS 3

TAKS 1

Teaching TipGalapagos Giant TortoisesTell students that the GalapagosIslands were named for the largetortoises that inhabit this archipel-ago. When Spanish explorersarrived, they found so many gianttortoises they called the islands“Galapagos,” Spanish for tortoise.The scientific name for the tortoisesis Geochelone elephantopus.Galapagos tortoises can weigh upto 227 kg (550 lb) and measure150 cm (5 ft) across the carapace(the upper shell). Galapagos tor-toises metabolize fat stored in theirtissues and, therefore, can survivewithout food or water for longperiods of time. Because of thischaracteristic, they became a con-venient source of fresh meat forearly explorers. The explorerscaught the tortoises on land andstored them live in ship holds forup to a year. When the Spanisharrived, there were an estimated250,000 tortoises. Today, approxi-mately 15,000 remain. Bio 3F

Teaching TipLaw of Use and Disuse Point out to students that Lamarck recognized that the environmentplayed an important role in evolu-tion. He theorized that when anorganism uses a part of its body,that part becomes more developedas a result of its use. He reasonedthat the modified part is thenpassed on to the organism’s off-spring. For example, he might haveargued that a bird that eats toughseeds will develop a thicker beakand will in turn have offspring with thicker beaks. Tell studentsthat if Lamarck were correct, theoffspring of bodybuilders would be born with enormously developed muscles. TAKS 1 IPC 3A,Bio 3A, 3F

TeachTeach

Chapter 13 • The Theory of Evolution 277

Science Before Darwin’s VoyageIn Darwin’s time, most people—including scientists—held the viewthat each species is a divine creation that exists, unchanging, as itwas originally created. But scientists had begun to seek to explainthe origins of fossils. Some scientists tried to explain their observa-tions by altering traditional explanations of creation. Others(including Darwin’s own grandfather) proposed various mecha-nisms to explain how living things change over time.

In 1809, the French scientist Jean Baptiste Lamarck (1744–1829)proposed a hypothesis for how organisms change over generations.Lamarck believed that over the lifetime of an individual, physicalfeatures increase in size because of use or reduce in size because ofdisuse. Further, according to Lamarck, these changes are thenpassed on to offspring. This part of Lamarck’s hypothesis is nowknown to be incorrect. However, Lamarck correctly pointed outthat change in species is linked to the “physical conditions of life,”referring to an organism’s environmental conditions.

Darwin’s ObservationsDuring his voyage on the Beagle, Darwin found evidence that chal-lenged the traditional belief that species are unchanging. Duringthe voyage, Darwin read Charles Lyell’s book Principles of Geology.Lyell proposed that the surface of Earth changed slowly over manyyears. As Darwin visited different places, he also saw things that hethought could be explained only by a process of gradual change.For example, in South America, Darwin found fossils of extinctarmadillos. These fossilized animals closely resembled, but werenot identical to, the armadillos living in the area.

Atlantic Ocean

Europe Asia

Australia

South America

Africa

Indian Ocean

North America

Pacific Ocean

Galápagos Islands

HMS Beagle

Figure 2 The route of HMS Beagle. HMS Beaglesailed around the world alongthe route shown on this map.The purpose of the ship’s 5-year voyage was to survey thecoast of South America.

277

IPC Benchmark Mini Lesson

Biology/IPC Skills TAKS 1 IPC 1A: Demonstrate safepractices during field and laboratory investigations.Activity Take students on a field trip to a local park orwildlife area to conduct a bird survey. Have studentstry to write down as many different types of birds asthey can. Then, have them group them using physicalsimilarities and create their own classification system.

IPC Benchmark Fact

Have students design a simple and hypotheticalexperiment in which Lamarck’s theory of evolution—the inheritance of acquired characteristics—couldbe tested. They should ask questions, formulate atestable hypothesis, and suggest how they wouldconduct the experiment. If time permits and theexperiment is doable, have students carry out theirinvestigations. TAKS 1 Bio/IPC 2A

Using the FigureHave students examine Figure 3and describe the features of thefinches’ bills. Have studentsdescribe how each finch’s bill isadapted to the bird’s diet. (Forexample, the large ground finch’s billis thick and heavy, which enablesthese birds to crack open large seeds.)

Visual

Interactive Reading AssignChapter 13 of the Holt BiologyGuided Audio CD Program to helpstudents achieve greater success inreading the chapter. Auditory

Group Activity Influences on Darwin Assign stu-dents to work in small groups toresearch what scientific data andtheories may have influencedDarwin as he began conducting hisinvestigations into the mechanism ofevolution. Have one group collectinformation on George Cuvier, who developed the theory known ascatastrophism from his work on fos-sils. Have another group collectinformation on James Hutton, whodeveloped the theory known asgradualism from his work on geo-logical formations. Have a finalgroup collect information on CharlesLyell, who developed the theoryknown as uniformitarianism fromhis work on geological processes.Have each group prepare a presen-tation on its findings, includinginformation on each man’s workand how Darwin’s ideas were influ-enced by the work. Bio 3F; Bio/IPC 3C

Co-op Learning

LS

SKILLBUILDER

READINGREADING

TAKS 3 Bio 7A (grade 11 only), 7BLS

GENERAL

Teach, continuedTeach, continued

Trends in Field BiologyRole of Naturalist Most scientists today mustspecialize in one field. However, many of thegreat scientists of the past were called natural-ists—people who studied nature from a varietyof different perspectives. Darwin’s role on theBeagle was not just to study the native plantsand animals encountered at the ship’s manystops but to study the geology, climate, andpeople of those areas as well. In fact, his inter-est in geology led him to collect many fossils,some high in the Andes Mountains of SouthAmerica. Such findings helped to stimulate histhinking about how environments and organ-isms might have changed over time. Bio 3F; Bio/IPC 3C


Survival of the Fittest The most famousstatement describing Darwin’s theory, “survivalof the fittest,” did not appear in Darwin’s orig-inal work. The phrase was coined by anotherbiologist, Herbert Spencer, upon learning aboutDarwin’s theory. Darwin liked the phrase andused it to summarize his theory’s implications.Unfortunately, others misunderstood and mis-interpreted the phrase. Soon the meaning offittest was distorted to mean “most powerfulor worthy.” Political leaders and industrialistsused it to justify conquest, colonialism, andoppression under the guise of “natural law.” Bio 3F

Darwin visited the Galápagos Islands, located about 1,000 km (620mi) off the coast of Ecuador. Darwin was struck by the fact that manyof the plants and animals of the Galápagos Islands resembled thoseof the nearby coast of South America. Darwin later suggested thatthe simplest explanation for this was that the ancestors of Galápagosspecies such as those shown in Figure 3, migrated to the islands fromSouth America long ago and changed after they arrived. Darwin latercalled such a change “descent with modification”—evolution.

When Darwin returned from his voyage at the age of 27, he con-tinued his lifelong study of plants, animals, and geology. However,he did not report his ideas about evolution until many years later.During those years, Darwin studied the data from his voyage. AsDarwin studied his data, his confidence that organisms had evolvedgrew ever stronger. But he was still deeply puzzled about how evo-lution occurs.

Growth of PopulationsThe key that unlocked Darwin’s thinking about how evolution takesplace was an essay written in 1798 by the English economist ThomasMalthus. Malthus wrote that human populations are able to increase

faster than the food supply can. Malthus pointedout that unchecked populations grow by geometricprogression, as shown in Figure 4. Food supplies,however, increase by an arithmetic progression atbest, also shown in Figure 4. He suggested thathuman populations do not grow uncheckedbecause death caused by disease, war, and famineslows population growth.

The term population, as it is used in biology,does not only refer to the human population. Inthe study of biology, a consists of allthe individuals of a species that live in a specificgeographical area and that can interbreed.

population

Fruit eater

Insecteaters

Insect eater

Seedeater

Vegetariantree finch

Small insectivorous

tree finch

Cactusground finch

Largegroundfinch

South Americanwarbler finch

Figure 3 Darwin’s finches.Darwin discovered that thesefinches closely resembledSouth American finches.

Time

Geometric progressionArithmetic progression

Two Rates of Progression

Figure 4 Geometric andarithmetic progressions.The blue graph line showsuncontrolled populationgrowth, in which the numbersincrease by a multiplied con-stant. The red graph lineshows increased food supply,in which the numbers increaseby an added constant.

278

Student Edition TAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B TEKS Bio 7A, 7B

Teacher Edition TAKS Obj 1 IPC 3A TAKS Obj 2 Bio 6C TAKS Obj 3 Bio 7A, 7B TEKS Bio 3A, 3F, 6C, 7A, 7BTEKS Bio/IPC 3C; IPC 3A

pp. 278–279

to cure patients. Antibiotic resistance hasbecome a problem because of the widespreaduse of antibiotics, not only for treatment ofhuman diseases, but also for prevention of diseases in humans and domestic animals. With such widespread use, a mutation in a bacterium’s DNA that allows it to survive treat-ment will be perpetuated. Soon, bacteria withthese mutations may constitute the majority ofthe species alive. TAKS 2 Bio 6C; Bio 3F

Discussion Tell students that theterm “teleology” is the doctrine ofdesign which holds that the phe-nomena of life can be explained byconscious or purposeful causesdirected to definite ends. Tell themthat many people refer to adapta-tions in living things as havingevolved “in order to” accomplishsome goal. For example, someonemight say that “birds evolvedwings in order to fly.” Lead a class discussion of teleology andwhy this concept differs from evo-lution by natural selection. (Naturalselection acts on variation alreadypresent in a population — it does notinduce variation.)

Graphing Have students draw agraph with numerical data toreinforce the difference betweengeometric progression and arith-metic progression. Have studentsdraw a graph that depicts the pop-ulation size of both an animal andits primary food source over a 30-year time period. Have studentsconnect the points on their graphswith a line. Assume that at a partic-ular point in time (time “zero” onthe graph), there are 10 animals inthe population. The populationdoubles in size every 5 years. Forthe graph depicting the food source,tell students that at time “zero”there are 10 units of food in theanimal’s environment and that thefood supply increases by 10 unitsevery 5 years. Ask them which linedepicts a geometric progression.(the line depicting population size)Ask them which line depicts anarithmetic progression. (the linedepicting units of food) LogicalLS

GENERALBUILDERSKILL

TAKS 1 IPC 3A; Bio 3A

GENERALSKILLBUILDER

READINGREADING


Antibiotics are powerful drugs that have savedmany lives. Penicillin, the first antibiotic discov-ered, was observed to inhibit bacterial growthon Petri dishes by the scientist AlexanderFleming in 1928. Many other antibiotics havebeen discovered or synthesized since then. Inthe last several decades, the effectiveness ofantibiotics has become compromised by theevolution of antibiotic-resistant strains of manyspecies. Some diseases must now be treatedwith a “cocktail” of several different antibiotics

REAL WORLDREAL WORLDCONNECTIONCONNECTION

Evolution by Natural SelectionDarwin realized that Malthus’s hypotheses about human populationsapply to all species. Every organism has the potential to producemany offspring during its lifetime. In most cases, however, only a lim-ited number of those offspring survive to reproduce. ConsideringMalthus’s view and his own observations and experience in breedingdomestic animals, Darwin made a key association. Individuals thathave physical or behavioral traits that better suit their environment aremore likely to survive and will reproduce more successfully than thosethat do not have such traits. Darwin called this differential rate ofreproduction . In time, the number of individualsthat carry these favorable characteristics will increase in a popula-tion. And thus the nature of the population will change—a processcalled evolution.

Darwin further suggested that organisms differ from place to placebecause their habitats present different challenges to, and opportu-nities for, survival and reproduction. Each species has evolved andhas accumulated adaptations in response to its particular environ-ment. An is a feature that has become common in apopulation because the feature provides a selective advantage.

Publication of Darwin’s WorkIn 1844, Darwin finally wrote down his ideas about evolution and nat-ural selection in an early outline that he showed to only a fewscientists he knew and trusted. At about this time, both a newlypublished book that claimed thatevolution occurred, and Lamarck’shypotheses about evolution wereharshly criticized. Shrinking fromsuch controversy, Darwin put asidehis manuscript.

Darwin decided to publish after hereceived a letter and essay in June1858 from the young English natu-ralist Alfred Russel Wallace(1823–1913), who was in Malaysia atthe time. Wallace’s essay described ahypothesis of evolution by naturalselection! In his letter, he asked ifDarwin would help him get the essaypublished. Darwin’s friends arrangedfor a summary of Darwin’s manu-script to be presented with Wallace’spaper at a public scientific meeting.

adaptation

natural selection

www.scilinks.orgTopic: Natural SelectionKeyword: HX4128

Figure 5 Political cartoon of CharlesDarwin. This 1874 cartoon of Darwin witha monkeylike “ancestor” is an example ofhow some people ridiculed Darwinbecause of his work.

279



Modeling NaturalSelectionSkills AcquiredCollecting data, inter-preting, summarizing,evaluating

Teacher’s NotesRemind students that individu-als have two copies of eachgene, and most mutations codefor recessive traits, meaning thatthe genes are expressed only ifan individual has two copies.

Answers to Analysis1. the different things that can

happen to an organism if it is exposed to change in itsenvironment

2. Most mutations will be passed on because they areharmful only if an individualhas two copies.

3. The survivors avoided chancedeath (a “die” card) and twocopies of the mutation, whichis “lethal” when expressed.

4. sample answer: does not dis-tinguish between beneficialand harmful mutations; doesnot distinguish between livingand reproducing

TAKS 1 Bio/IPC 2B,2C; TAKS 3 Bio 7B;

Bio 3E

did you know?Charles Darwin’s grandfather, Erasmus Darwin,wrote about evolution more than 60 yearsbefore his grandson’s theory was presented.Erasmus Darwin cited things such as the meta-morphosis of insects, the new varieties producedby selective breeding, the variations among similar organisms in different climates, and thesimilarities of vertebrate structure as evidencethat all life was “produced from a similar livingfilament.” Unlike his famous grandson, ErasmusDarwin attributed change among organisms tothe inheritance of characteristics acquired eithernaturally or at the will of the organism. Bio 3F

StrategiesStrategiesINCLUSIONINCLUSION

Using a box of animal crackers, have thestudents select several different “animals.”For each of the “animals” selected, have thestudent describe and draw changes thatwould have to take place for each of these“animals” to evolve to live in a water envi-ronment. Also have the student describe anddraw changes if these “animals” had toevolve to an environment like that at theSouth Pole.

• Learning Disability• Attention Deficit Disorder

• Gifted and Talented

Darwin’s TheoryDarwin’s book On the Origin of Species by Means of Natural Selectionappeared in November of 1859. Many people were deeply disturbedby certain suggestions of Darwin’s theory, such as that humans arerelated to apes, as Figure 5 on the previous page suggests. But Darwin’sarguments and evidence were very convincing, and his view that evolu-tion occurs gained acceptance slowly from biologists around the world.

Darwin’s theory of evolution by natural selection is supported byfour major points:

Variation exists within the genes of every population or species(the result of random mutation and translation errors).

In a particular environment, some individuals of a populationor species are better suited to survive (as a result of variation)and have more offspring (natural selection).

Over time, the traits that make certain individuals of a populationable to survive and reproduce tend to spread in that population.

There is overwhelming evidence from fossils and many othersources that living species evolved from organisms that are extinct.

Modeling Natural SelectionBy making a simple model of natural selection you canbegin to understand how natural selection changes apopulation.

Materials

paper, pencil, watch or stopwatch

Student name Trial 1 Trial 2 Trial 3

DATA TTABLE

2B 2C 3E 7B

Procedure

1. On a chalkboard or overheadprojector, make a data tablelike the one shown below.

2. Write each of the followingwords on separate pieces ofpaper: live, die, reproduce,mutate. Fold each piece ofpaper in half twice so that youcannot see the words. Shuffleyour folded pieces of paper.

3. Exchange two of your piecesof paper with those of aclassmate. Make as manyexchanges with additionalclassmates as you can in 30seconds. Mix your pieces ofpaper between eachexchange you make.

4. Look at your pieces of paper.If you have two pieces thatsay “die” or two pieces thatsay “mutate,” then sit down.If you do not, then you are a“survivor.” Record yourresults in your class table.

5. If you are a “survivor,” recordthe words you are holding inthe data table. Then refoldyour pieces of paper andrepeat steps 2 and 3 two moretimes with other “survivors.”

Analysis

1. Identify what the four slipsof paper represent.

2. Describe what happens tomost mutations in this model.

3. Identify what factor(s)determined who “survived.”Explain.

4. Evaluate the shortcomingsof this model of naturalselection.

280

TAKS 1, TAKS 3

Student Edition TAKS Obj 1 Bio/IPC 2B, 2C TAKS Obj 2 Bio 6C TAKS Obj 3 Bio 7B TEKS Bio 3E, 6C, 7B; Bio/IPC 2B, 2C

Teacher Edition TAKS Obj 2 Bio 6D TAKS Obj 3 Bio 7A TEKS Bio 3F, 6D, 7A

pp. 280–281

Math Skills Provide students withthe information contained in theMath Connection: Hardy WeinbergEquilibrium at the bottom of thispage. Tell them to consider theexample of a flowering plant inwhich red color is dominant (“A”allele) and white color is recessive(“a” allele). Have them consider apopulation of 100 of these plants,of which 16 are white-flowered(“aa” genotype). Have them calcu-late the frequencies of the A allele(frequency � p) and the a allele(frequency � q). (Since q2 is the frequency of the aa genotype, and q2 � 0.16 [16/100], then q � 0.4 andp � 0.6.) Next, tell students thatafter a period of time there aren’tas many white-flowered plantsaround—only 4 out of 100 plants.Ask them what the new frequenciesof the A allele and a allele are. (q2 � 0.04, so q � 0.2 and p � 0.8.)

Logical TAKS 2 Bio 6D (grade 11only)

Demonstration Bring to class as many of the fol-lowing food crops as possible:cabbage, Brussels sprouts, broccoli,cauliflower, kale, and kohlrabi. Tryto bring a wild mustard plant or apicture of one. (This can be foundin many biology and horticulturetexts.) Point out the parts of theplants that are eaten. Tell studentsthat all of these different varietieshave been bred from the samespecies, Brassica oleracea. Ask stu-dents how these varieties of thesame species could look so differ-ent. (There is so much variation inthe genes of this species.) Is it possi-ble for these varieties to becomeseparate species? (yes) How?(Through isolation, their geneticmake-ups may become so differentthat they can no longer interbreed.)TAKS 2 Bio 6D (grade 11 only); TAKS 3Bio 7A (grade 11 only)

LS

BUILDERSKILL


The frequency of one plus the frequency of theother must equal 100%, or p � q � 1. Thechances of all possible combinations of allelesoccurring randomly is therefore (p � q)2 � 1,or more simply, p2 � 2pq � q2 � 1. In thisequation, p2 is the frequency of homozygousdominant (AA) individuals in a population,2pq is the frequency of heterozygous (Aa) indi-viduals, and q2 is the frequency of homozygousrecessive (aa) ones. Bio 3F

In 1908, two scientists named Hardy andWeinberg developed a simple equation that canbe used to determine the genotype frequenciesin a population and to track their changes fromone generation to another. This is known as the“Hardy-Weinberg equilibrium equation.” Inthis equation (p2 � 2pq � q2 � 1), p is definedas the frequency of the dominant allele and qas the frequency of the recessive allele for atrait controlled by a pair of alleles (A and a).

MATHMATHCONNECTIONCONNECTION

Darwin’s Ideas UpdatedSince the time Darwin’s work was published, his hypothesis—thatnatural selection explains how evolution happens—has been care-fully examined by biologists. New discoveries, especially in the areaof genetics, have given scientists new insight into how natural selec-tion brings about the evolution of species. Darwin’s ideas, restatedin modern terms, are summarized here.

Change Within PopulationsDarwin’s key inference was based on the idea that in any popula-tion, individuals that are best suited to survive and do well in theirenvironment will produce the most offspring. So, the traits of thoseindividuals will become more common in each new generation.

Scientists now know that genes are responsible for inheritedtraits. Therefore, certain forms of a trait become more common ina population because more individuals in the population carry thealleles for those forms. In other words, natural selection causes thefrequency of certain alleles in a population to increase or decreaseover time. Mutations and the recombination of alleles that occursduring sexual reproduction provide endless sources of new varia-tions for natural selection to act upon.

Species FormationThe environment differs from place to place. Thus, populations of thesame species living in different locations tend to evolve in differentdirections. is the condition in which two pop-ulations of the same species do not breed with one another becauseof their geographic separation. As two isolated populations of thesame species become more different over time, they may eventuallybecome unable to breed with oneanother. Generally, when the individu-als of two related populations can nolonger breed with one another, thetwo populations are considered to be different species. As shown inFigure 6, the Kaibab squirrel, whichlives on the North Rim of the GrandCanyon in Arizona, has a black bellyand other characteristics that distin-guish it from the Abert squirrel. TheAbert squirrel, which has a white belly,lives on the South Rim of the GrandCanyon. Because they have been soisolated from one another, they havebecome different enough that biolo-gists consider them separate species.

Reproductive isolation

www.scilinks.orgTopic: Theory of EvolutionKeyword: HX4175

Kaibab squirrel Abert squirrel

These two squirrel populations became isolated from each otherabout 10,000 years ago, thus preventing their interbreeding.

Figure 6 Reproductive isolation in action

281

ReteachingRemind students that while Wallacewas in Indonesia, he wrote a paperdescribing his idea about howevolution occurred and sent it toDarwin. Ask students to write a let-ter that Darwin could have writtento Wallace in response. Verbal

Quiz1. What is a feature called that

provides a selective advantage toa population? (An adaptation)

2.At what level does evolution of organisms occur? (the popula-tion level)

AlternativeAssessmentHave students make visual representations of the four majorpoints that support Darwin’s theory.For example, for point 1 studentscould cut out pictures of differentindividuals of the same species andpaste them onto the board. Belowthe pictures, they could list possiblevariations in the traits of the species. KinestheticLS

GENERAL

GENERAL

LS

CloseClose

Answers to Section Review

1. Darwin found fossils of armadillos that closelyresembled living armadillos. He also observedthe resemblance between organisms on theGalapagos Islands and those on the nearestcoast. Bio 3C, 3F

2. Individuals with traits well-suited to theirenvironment are more likely to survive andreproduce than individuals without such traits.TAKS 3 Bio 7B

3. Genetic variations in a population enable someorganisms to produce more offspring than oth-ers. Over time, populations evolve and reflectthe survival of organisms with the most advan-tageous heritable traits. TAKS 1 IPC 3A; Bio 3A

4. According to the punctuated equilibriummodel, evolution occurs in spurts in responseto strong environmental pressures. Accordingto gradualism, species evolve gradually overlong periods of time. TAKS 1 IPC 3A; Bio 3A, 3E

5. A. Incorrect. Extinct populationscannot be acted upon by natural selection. B.

Correct. Isolation prevents interbreeding. C.

Incorrect. If two populations are interbreeding,they will not diverge into different species. D.

Incorrect. A single population of a species willremain a single species unless isolation occurs.TAKS 3 Bio 7B


Punctuated EquilibriumTeaching StrategiesExplain that these models arejust that: abstractions thatdescribe and help us understandthe mechanics of evolutionarychange. Emphasize that a goodscientist tries to make a modelfit his or her research results,not the other way around.

The Tempo of EvolutionFor decades, most biologists have understood evolution as a gradu-al process that occurs continuously. The model of evolution inwhich gradual change over a long period of time leads to speciesformation is called . But American biologists StephenJay Gould and Niles Eldredge have suggested that successfulspecies may stay unchanged for long periods of time. Gould andEldredge have hypothesized that major environmental changes inthe past have caused evolution to occur in spurts. This model ofevolution, in which periods of rapid change in species are separatedby periods of little or no change, is called .punctuated equilibrium

gradualism

Punctuated Equilibrium

How could major environmental changes lead tospurts in evolution? The fossil record shows thatdrastic environmental changes have occurred veryinfrequently, separated by periods of time thatoften last tens of millions of years. Events such asvolcanic eruptions, asteroid impacts, and ice ageshave been linked to sudden and drastic changesin climate. Such changes have also been linked tothe extinction of many groups of organisms. As aresult, environments that were once inhabitedbecame empty. This provided opportunities forcolonization by species that could quickly adaptto the new conditions through natural selection.

What Fossils RevealAlthough there are large gaps in the fossil record asa result of erosion and other destructive geologicprocesses, the fossil record seems to provideevidence of both gradualism and punctuatedequilibrium. Many groups of organisms appearsuddenly in the fossil record. Some of these groupsremain virtually unchanged for millions of years,while other groups disappear as suddenly as they

appear. Still other groups of organisms appear tochange slowly through time, as predicted by thegradualism model of evolution. More study of thefossil record may reveal additional examples of oneor both types of evolution.

FurtherExploring Further

Gradualism Punctuated equilibrium

List two observations made by Charles Darwinduring his 5-year voyage that led him to concludethat living species evolved from extinct species.

Describe how natural selection occurs. 7B

Summarize the modern theory of evolution bynatural selection. 3A

Compare the punctuated equilibrium model ofevolution with the gradualism model. 3A 3E

Speciation can result when twopopulations have become A extinct. C interbred.B reproductively isolated. D one population.

TAKS Test PrepTAKS Test Prep

Section 1 Review

www.scilinks.orgTopic: Fossil RecordKeyword: HX4088

3C 3F

7B

www.scilinks.orgTopic: EvolutionKeyword: HX4074

282

Student Edition TAKS Obj 1 IPC 3A TAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B TEKS Bio 3A, 3E, 3F, 7A, 7B;Bio/IPC 3C; IPC 3A

Teacher Edition TAKS Obj 3 Bio 7A TEKS Bio 3F, 7A

pp. 282–283

Section 2

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. Tell students that the pur-pose of this lesson is to teach themabout the different types of infor-mation scientists have found thatprovide evidence of evolution.These include the fossil record;molecular similarities in proteinsand nucleic acids; anatomical simi-larities among organisms; andsimilarities among developmentalpatterns of organisms.

Bring in several fossils and passthem around to student groups. Ask students to brainstorm whatorganisms they think the fossilsrepresent. Examples of fossilsinclude fossilized bones, shells,footprints, or leaf prints. You canthen start the lesson by discussingwhat fossils are and how they formed. TAKS 3 Bio 7A (grade 11only)

Discussion/QuestionRead the following passage fromDarwin’s On the Origin of Species:“Of this history [of the world], wepossess the last volume alone… Ofthis volume, only here and there ashort chapter has been preserved;and of each page, only here andthere a few lines.” Ask students todescribe what Darwin meant bythis passage. (Darwin was referringto the incompleteness of the fossilrecord unearthed so far.) VerbalBio 3F

LS

GENERAL

MotivateMotivate

Bellringer

FocusFocus


• Lesson Plan• Directed Reading• Active Reading GENERAL

GENERAL

Chapter Resource File

Transparencies

TT BellringerTT Evidence of Whale EvolutionTT Forelimbs of VertebratesTT Hemoglobin Comparison

• Reading Organizers• Reading Strategies • Supplemental Reading

The Origin of Species

Planner CD-ROM

The Fossil Record Have you ever looked at a series of maps that show how a city hasgrown? Buildings and streets are added, changed, or destroyed asthe years pass by. In the same way, fossils of animals show a patternof development from early ancestors to modern descendants. Fos-sils offer the most direct evidence that evolution takes place. Recallthat a fossil is the preserved or mineralized remains or imprint ofan organism that lived long ago. Fossils, therefore, provide anactual record of Earth’s past life-forms. Change over time (evolu-tion) can be seen in the fossil record. Fossilized species found inolder rocks are different from those found in newer rocks, as youcan see in Figure 7.

After observing such differences, Darwin predicted that interme-diate forms between the great groups of organisms would eventuallybe found. Since Darwin’s time, many of these intermediaries havebeen found. For example, fossil intermediaries have been foundbetween fishes and amphibians, between reptiles and birds, andbetween reptiles and mammals, adding valuable evidence about thefossil history of the vertebrates.

Today, Darwin’s theory is almost universally accepted by scien-tists as the best available explanation for the biological diversity onEarth. Based on a large body of supporting evidence, most scien-tists agree on the following three major points:

1. Earth is about 4.5 billion years old.

2. Organisms have inhabited Earth for most of its history.

3. All organisms living today share common ancestry with earlier, simpler life-forms.

Evidence of Evolution Section 2

Objectives● Describe how the fossil

record supports evolution.

● Summarize how biologicalmolecules such as proteinsand DNA are used as evidence of evolution.

● Infer how comparing theanatomy and developmentof living species providesevidence of evolution.

Key Terms

paleontologistvestigial structurehomologousstructure

Figure 7 Fossils. Fossils of early multicellular life-forms,such as the crinoid, occur in 800-million-year-old rocksfound in Indiana. Fossils of the pterodactyl, an extinctreptile, occur in 140- to 210-million-year-old rocks.

Crinoid Pterodactyl

7A

9A

7A

283

TAKS 3

TAKS 3

Teaching TipExtinct Organisms Tell studentsthat scientists estimate that 99 per-cent of all animal and plant speciesthat ever existed are now extinct.Most people do not realize howmany species have been found bypaleontologists. In the past fewyears, many new species have been discovered. For example, inone small area in Wyoming, earlyEocene rocks have yielded fossils ofmore than 50 species of animals.

Using the Figure Tell students that the first three ani-mals in Figure 8 are known onlyfrom their fossil remains. Thefourth animal is a living species.Note that the backbone of theRodhocetus kasrani skeleton is notcomplete, as the tailbones shown ingray indicate. Tell students that it israre to find a complete skeleton inany one fossil. As more skeletons of this species are found, all thespecies’ bones may eventually befound. Using their knowledge ofanatomy, paleontologists projectwhat these bones will look like.Ask students how the backbonechanged relative to the time theseanimals spent in water. (The back-bone became heavier.) What is theadvantage of this change? (Whalesuse up-and-down motions of theirbodies to swim. A heavier backbonebetter supports the muscles used forthis motion.) VisualLS

GENERAL

TeachTeach

it decays, causing the ratio of carbon-14 to carbon-12 to decrease over time. If a fossilizedorganism has one-fourth the carbon-14 to carbon-12 ratio of a living organism, the fossilis 11,460 years old. (This is two half-lives ofcarbon-14.) Because the half-life of carbon-14is relatively short, this radioisotope is only used for dating fossils and artifacts less thanabout 50,000 years old. To date older fossils,scientists use radioactive isotopes with longerhalf-lives. For example, uranium-235 has ahalf-life of 704 million years. IPC 8D


Scientists can determine the ages of fossils andother artifacts by measuring the amount ofdecay of radioactive atoms in the specimen orin the surrounding sediment. Since a radioac-tive atom is unstable, it will eventually changeinto a more stable atom. The term half-lifedescribes how long it takes for one-half of theradioactive atoms in a sample to decay. Forexample, the half-life of carbon-14 is 5,730years. (The most common form of carbon inliving things is carbon-12.) When an organismdies, the carbon-14 it has steadily decreases as

CHEMISTRYCHEMISTRYCONNECTIONCONNECTION

Formation of FossilsThe fossil record, and thus the record of the evolution of life, is notcomplete. Many species have lived in environments where fossils donot form. Most fossils form when organisms and traces of organ-isms are rapidly buried in fine sediments deposited by water, wind,or volcanic eruptions. The environments that are most likely tocause fossil formation are wet lowlands, slow-moving streams,lakes, shallow seas, and areas near volcanoes that spew out volcanicash. The chances that organisms living in upland forests, moun-tains, grasslands, or deserts will die in just the right place to beburied in sediments and fossilized are very low. Even if an organismlives in an environment where fossils can form, the chances are slimthat its dead body will be buried in sediment before it decays. Forexample, it may be eaten and scattered by scavengers. Furthermore,

Ambulocetus natans apparently walked on landlike modern sea lions and swam by flexing itsbackbone and paddling with its hind limbs (as domodern otters). They were about 3 m (10 ft) long.They existed about 50 million years ago.

Mesonychids are one hypothesized link betweenmodern whales and certain hoofed mammals.They were about 2 m (6 ft) long. They are thoughtto have lived about 60 million years ago. Somescientists favor an alternative hypothesis linkingwhales to other ancestral hooved mammals.These hooved mammals are also ancestral tohippopotamuses or pigs.

Whales are thought to have evolved from an ancestral line of four-legged mammals, which are represented here by their fossils and artistic reconstructions showing what scientists think they may have looked like.

Figure 8 Evidence of whale evolution

Reading EffectivelyRead the heading “Forma-tion of Fossils,” and ask oneor more Who, What, Where,When, Why, or How ques-tions. For example, How arefossils formed? As you read,answer your questions.

284

Student Edition TAKS Obj 3 Bio 7A TEKS Bio 7A

Teacher Edition TAKS Obj 3 Bio 7A, 7B TEKS Bio 7A, 7B; IPC 8D

pp. 284–285

Teaching TipPenguins “Fly” UnderwaterTell students that, although pen-guins are not able to fly in the air,the movement of their wings underwater resembles the motion of thewings of birds that do fly. However,penguins have much heavier bonesthan birds that fly in the air. Askstudents what adaptive advantagethis might give penguins. (The heftybone structure of a penguin’s wings isan advantage for moving throughwater, which is far denser than air.Also, heavier bones are not a disad-vantage because of the buoyancy provided by water.) TAKS 3 Bio 7B

Demonstration Have students study samples orpictures of different types of fossils.Ask how these organisms are simi-lar to modern organisms. (Answerswill vary. Students should note thesimilarities in bone and shell struc-ture.) Diatomaceous earth used inaquarium filters provides excellentexamples of microfossils forexamination. Visual TAKS 3Bio 7A (grade 11 only)

LS

GENERAL


MISCONCEPTION ALERT

A discussion of vestigial structures begins onthe next page. Many people think that struc-tures are labeled as vestigial because they areuseless. Many such structures do, in fact,have functions. Structures are labeled vestig-ial if they are smaller, less functional, orperform a different function from that of

homologous structures in ancestral life forms.For example, the yolk sac of a mammal ishomologous to the yolk sac of birds and rep-tiles, but it is considered vestigial because itdoes not provide nutrients for the growingembryo. However, the mammalian yolk sacdoes produce blood cells.

the bodies of some organisms decay faster than others do. Forexample, an animal with a hard exoskeleton (such as a crab) wouldhave a better chance of becoming fossilized than would a soft-bodied organism, such as an earthworm.

Although the fossil record will never be complete, it presentsstrong evidence that evolution has taken place. , sci-entists who study fossils, can determine the age of fossils fairlyaccurately by using radiometric dating. Radiometric dating thesediments in which a fossil is found enables paleontologists toarrange fossils in sequence from oldest to youngest. When this isdone, orderly patterns of evolution can be seen. Based on existingfossils, Figure 8 shows an artist’s idea of the appearance of threeextinct species that might have been ancestral to modern whales.They are arranged in the order that they evolved, based on theirfossil’s age as determined by radiometric dating.

Paleontologists

Modern whales have forelimbs that are flippersand hind limbs that have been reduced to only afew internal functionless hind-limb bones.

Rodhocetus kasrani, a more recent ancestor ofmodern whales, probably spent little time on land.Its reduced hind limbs could not have aided inwalking or swimming. It is thought to have existedabout 40 million years ago.

www.scilinks.orgTopic: PaleontologyKeyword: HX4134

285

Teaching TipMaking Mutations To show stu-dents that the amino acid sequenceof a protein is determined by thenucleotide sequence of a gene, put the following sequence ofnucleotide bases on the board oroverhead: CUU, GUU, CCU, GGC,AGG. Have students look up theamino acids encoded by thesetriplets. (leucine, valine, proline,glycine, and arginine) Have studentstake turns substituting one of theother three nitrogen bases for abase in one of the triplets. Havestudents look up the name of theamino acid encoded by the newtriplet. Tell students that the substitu-tions they made represent mutations.Ask how mutations affect the pro-teins encoded by DNA. (Mutationschange the proteins produced bychanging the blueprints for theirproduction.)

Using the Figure Direct students’ attention toFigure 10. Ask them which specieslisted in this table shares the mostrecent common ancestor withhumans. (gorilla) Ask them if afamily tree produced with theamino acid data in Figure 10 wouldshow the same relationships as afamily tree based on nucleotidesubstitutions. (yes) Why? (Anucleotide sequence determines anamino acid sequence.) TAKS 3 Bio 7A(grade 11 only), 7B

GENERAL

TAKS 2 Bio 6C; Bio 9A

GENERAL



Graphic Organizer

Use this graphic organizer withReteaching on the next page.

Homologousstructures

Birds HumansDolphins

Whales

Molecules

Vertebrates

Mice

Chickens Frogs

LampreysRhesus monkeys

EvolutionVestigial

structures

Proteins

Pelvis

Forelimbs

Anatomy and Development Comparisons of the anatomy of different types of organisms oftenreveal basic similarities in body structures even though the structure’sfunctions may differ between organisms. For example, sometimesbones are present in an organism but are reduced in size and eitherhave no use or have a less important function than they do in other,related organisms. Such structures, which are considered to beevidence of an organism’s evolutionary past, are called (vehsTIJ ee uhl) . For example, the hind limbs of whales are ves-tigial structures.

As different groups of vertebrates evolved, their bodies evolveddifferently. But similarities in bone structure can still be seen,suggesting that all vertebrates share a relatively recent commonancestor. As you can see in Figure 9, the forelimbs of the vertebratesshown are composed of the same basic groups of bones. Such struc-tures are referred to as homologous (hoh MAHL uh guhs).

are structures that share a common ances-try. That is, a similar structure in two organisms can be found in thecommon ancestor of the organisms.

The evolutionary history of organisms is also seen in the devel-opment of embryos. At some time in their development, allvertebrate embryos have a tail, buds that become limbs, and pha-ryngeal (fuh RIN jee uhl) pouches. The tail remains in most adultvertebrates. Only adult fish and immature amphibians retainpharyngeal pouches (which contain their gills). In humans, the taildisappears during fetal development, and pharyngeal pouchesdevelop into structures in the throat.

Homologous structures

structuresvestigial

The word vestigial comesfrom the Latin word ves-tigium, meaning “footprint.”Homologous is from theGreek word homologos,meaning “agreeing.”

The forelimbs of vertebrates contain the same kinds of bones, which form in thesame way during embryological development.

Figure 9 Homologous structures

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Penguin Alligator

HumanBat

286

Student Edition TAKS Obj 2 Bio 6C TAKS Obj 2 Bio 6D TAKS Obj 3 Bio 7A TEKS Bio 6C, 6D, 7A, 8B, 9A

Teacher Edition TAKS Obj 1 IPC 3A TAKS Obj 2 Bio 6C TAKS Obj 3 Bio 7A, 7B TEKS Bio 3A, 6C, 7A, 7B, 8B, 9A; IPC 3A

pp. 286–287

4. A. Incorrect. These two animalsshould have relatively similar nucleotidesequences because they are both primates andthus closely related. B. Incorrect. These twoanimals should have somewhat similarnucleotide sequences because they are bothmammals. C. Incorrect. These two animals areboth vertebrates and should have nucleotidesequences that are more similar than those of avertebrate (shark) and invertebrate (butterfly).D. Correct. The shark is a vertebrate, and thebutterfly is an invertebrate. They are the leastrelated and would have the least similarnucleotide sequences. TAKS 2 Bio 6D; Bio 8B

ReteachingHave students design a GraphicOrganizer that describes two kindsof physical traits that can be usedto support the theory of evolutionby natural selection. Logical

Quiz1. What does the presence of hind

limb remnants in the whale indi-cate? (The presence of these bonesindicates that whales evolved froma land-dwelling ancestor.)

2.What is a vestigial structure?(bones or other structures that arepresent in an organism but arereduced in size and either have no use or have a less importantfunction than they do in other,related organisms)

AlternativeAssessmentTell students that the earliest phylo-genetic diagrams were constructedusing only evidence of morphologi-cal characteristics. Ask students whysuch diagrams might not reflect trueevolutionary relationships. (Similarmorphological characteristics mightreflect adaptation to a similar environ-ment, rather than a common ancestry.)Have students use library resourcesto construct phylogenetic diagrams of an organism or organisms oftheir choosing. Remind them toconsider more than morphologicalcharacteristics. Bio 8B

GENERAL

LS

CloseClose


Biological MoleculesThe picture of successive change seen in the fossil record allows sci-entists to make a prediction that can be tested. If species havechanged over time as the fossil record indicates, then the genes thatdetermine the species’ characteristics should also have changed bymutation and selection. As species evolved, one change after anothershould have become part of their genetic instructions. Therefore,more and more changes in a gene’s nucleotide sequence should buildup over time.

ProteinsThis prediction was first tested by analyzing the amino acidsequences of similar proteins found in several species. Recall thatthe amino acid sequence of proteins is genetically determined. Ifevolution has taken place, then species descended from a recentcommon ancestor should have fewer amino acid differencesbetween their proteins than do species that shared a common ances-tor in the distant past.

Comparing one human hemoglobin protein with the same hemo-globin protein of other species reveals the predicted pattern, asshown in Figure 10. Species that shared a common ancestor morerecently (for example, humans and gorillas) have few amino acidsequence differences. However, those species that share a commonancestor in the more distant past (such as gorillas and frogs) havemany amino acid sequence differences.

Nucleic AcidsAs you have read in an earlier chapter, nucleotide changes (such asnucleotide substitutions) cause changes in the amino acid sequenceof a protein. Scientists evaluate the number of nucleotide changesthat have taken place in a gene since two species diverged from acommon ancestor by comparing the nucleotide sequence of genes.Using the data obtained from proteins and nucleotides, scientistsgenerate hypotheses about how organisms are related through evo-lution. The hypotheses, based on molecular data, tend to reflect therelationships indicated by the fossil record.

Hemoglobin Comparison

Species Amino AcidDifferencesfrom HumanHemoglobinProtein

Gorilla 1

Rhesus monkey 8

Mouse 27

Chicken 45

Frog 67

Lamprey 125

Figure 10 Hemoglobindifferences. The more similar organisms’ hemoglobinproteins are, the more recentthe organisms’ commonancestor is likely to have been.

Section 2 Review

Relate how the fossil record provides evidencethat evolution has occurred. 7A

State how comparing the amino acid sequenceof a protein can provide evidence that evolutionhas taken place. 9A

Describe how comparing the anatomy of livingspecies provides evidence of evolution. 7A

Which two organisms wouldlikely have the least-similar nucleotide sequencesin a given gene? 6D 8B

A chimpanzee and gorillaB gorilla and dogC dog and sharkD shark and butterfly


287

Bio 9A

IPC BenchmarkFact

Ask students to analyze, review, and critique the evidence marshaled in sup-port of the theory of evolution. Theyshould consider the strengths andweaknesses of the fossil evidence,amino acid sequence differences,nucleotide substitutions, vestigial struc-tures, homologous structures, andembryo development. Have studentsdiscuss and rank the evidence fromstrongest to weakest and justify theirrankings. TAKS 1 IPC 3A; Bio 3A


1. Answers will vary. The fossil record showschanges in organismal forms that can be tracedforward and backward in time along differentancestral lines. TAKS 3 Bio 7A (grade 11 only)

2. Similarities in amino acid sequences suggestthat organisms are related, and may indicatethe degree of relatedness. Differences in aminoacid sequences suggest that mutations haveintroduced genetic variation into populations oforganisms that eventually resulted in evolution.

3. Anatomical similarities between living species,such as similar bones used for similar func-tions, suggest that these species may haveevolved from a common ancestor. TAKS 3 Bio7A(grade 11 only)

OverviewBefore beginning this sectionreview with your students theobjectives listed in the StudentEdition. This lesson provides exam-ples of population changes that haveresulted from natural selection. Italso describes how the process ofevolution may result in the forma-tion of new species.

Have student groups brainstorm toidentify characteristics of birds thatprovide information about theirdiets. (This information could beinferred from beak characteristics. A large, anvil-like beak suggests a dietof large seeds. A long, narrow beaksuggests a diet of insects or possiblynectar. A very large claw-like beaksuggests a diet of the flesh of animals.)TAKS 2 Bio 8C

Discussion/QuestionPoint out that within the phylumArthropoda, the class Insecta hasmore species than any other class.In fact, about one-third of all ani-mals are beetles, which constitutejust one order of insects. To date,more than 1 million species ofinsects have been classified, andmany scientists estimate that thereare probably several million more.Ask students how they think somany different kinds of species ofinsects could have evolved. (Insectsare adapted to many different kindsof environments and rely on manydifferent kinds of food sources.) TAKS 3 Bio 7B

GENERAL

MotivateMotivate

Bellringer

FocusFocus

Section 3


Pg. 288: 7A, 7B

• Reading Organizers• Reading Strategies

Planner CD-ROM

Transparencies

TT BellringerTT Beak Size VariationTT Mating Activity in Raven Species

• Lesson Plan• Directed Reading• Active Reading• Data Sheet for Math Lab GENERAL

GENERAL

GENERAL


Section 3 Examples of Evolution

Natural Selection at WorkHow does evolution occur? The heart of Darwin’s theory of evolu-tion is that natural selection is the mechanism that drives evolution.Darwin wrote: “Can we doubt . . . that individuals having any advan-tage, however slight, over others, would have the best chance ofsurviving and of procreating their kind? On the other hand, we mayfeel sure that any variation in the least degree injurious would berigidly destroyed. This preservation of favorable variations, I callNatural Selection.” In his writings, Darwin offered examples of hownatural selection has shaped life on Earth. There are now manywell-known examples of natural selection in action.

The key lesson scientists have learned about evolution by nat-ural selection is that the environment dictates the direction andamount of change. If the environment changes in the future, theset of characteristics that most help an individual reproduce suc-cessfully may change. For example, the polar bear’s white fur,shown in Figure 11, enables it to hunt successfully in its snowyenvironment. In a warmer environment, having white fur wouldno longer be an advantage.

Factors in Natural SelectionThe process of natural selection is driven by four important pointsthat are true for all real populations:

All populations have genetic variation. That is, in any popu-lation there is an array of individuals that differ slightly fromeach other in genetic makeup. While this may be obvious inhumans, it is also true in species whose members may appearidentical, such as a species of bacteria.

The environment presents challenges to suc-cessful reproduction. Naturally, an organismthat does not survive to reproduce or whose off-spring die before the offspring can reproducedoes not pass its genes on to future generations.

Individuals tend to produce more offspringthan the environment can support. Thus indi-viduals of a population often compete with oneanother to survive.

Individuals that are better able to cope withthe challenges presented by their environmenttend to leave more offspring than those indi-viduals less suited to the environment do.

Objectives● Identify four elements in the

process of natural selection.

● Describe how natural selection has affected thebacteria that causetuberculosis.

● Relate natural selection tothe beak size of finches.

● Summarize the process ofspecies formation.

Key Terms

divergencespeciationsubspecies

Figure 11 Polar bear.Camouflage benefits predatorsand prey alike.

7B

7B

7A

7B

288

Student Edition TAKS Obj 2 Bio 4D TAKS Obj 2 Bio 6C TAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B TEKS Bio 4D, 6C, 7A, 7B

Teacher Edition TAKS Obj 2 Bio 6D TAKS Obj 3 Bio 7A, 7B TEKS Bio 6D, 7A, 7B; Bio/IPC 3C

pp. 288–289

IPC Benchmark Review

To prepare students for the TAKS and accompany the discussion of fossils, have students review TheRock Cycle TAKS 4 IPC 8A on pp. 1052–1053 of the IPC Refresher in the Texas Assessment Appendix ofthis book.

TAKS 3

TAKS 3

TAKS 3

TAKS 3

Teaching TipSelection Pressure and Rates ofEvolution Tell students that theterm selection pressure refers to theimpact of natural selection on aparticular trait. If individualsexpressing a particular trait all diebefore they reach reproductive age,then we say that there is verystrong selection pressure againstthat trait. An example is the humandisease cystic fibrosis, whose vic-tims have until only recently rarelysurvived to reproductive age. Anallele that has strong selection pres-sure against it is not likely to persistin a species. However, if the trait isrecessive, as it is for cystic fibrosis,individuals who are heterozygouswill not be subjected to selectionpressure themselves but will passthe allele on to future generations.In this way, harmful alleles can per-sist for a long time in a species.TAKS 2 Bio 6D; TAKS 3 Bio 7B

Group ActivityExamples of Evolution Havestudents work in small groups toresearch examples of evolutionusing library, Internet, or othersources. Their examples shouldshow evolutionary change within ahuman lifespan. Assign one groupto work on examples of artificialselection by humans. This groupcould select examples amongdomestic and farm animals, or cropplants. Assign a second group towork on examples of selection inbacteria resulting from human useof antibiotics. This group couldselect examples among pathogenicbacteria. Assign a third group towork on examples of animal selec-tion in laboratory organisms. Thisgroup could select examples oforganisms such as Neurospora,Drosophila melanogaster, or smallrodents. Have each group preparean illustrated poster displayingtheir findings. Display the postersfor the whole class to examine.

TAKS 3 Bio 7BCo-op Learning

GENERAL

TeachTeach


Natural selection has made insect pestsharder to fight. When DDT was first intro-duced, for example, it was a highly effectiveinsecticide. Over time, DDT became less andless effective; individuals that were resistantto the insecticide survived and produced thenext generation. In fact, many populations ofinsects are now resistant to DDT. AlthoughDDT is now banned in the United Statesbecause of its persistent toxicity, farmers haverepeatedly had to deal with insect popula-tions that develop resistance to insecticides.TAKS 3 Bio 7A (grade 11 only), 7B; Bio/IPC 3C

TECHNOLOGYTECHNOLOGYCONNECTIONCONNECTIONStrategiesStrategies

INCLUSIONINCLUSION

Using the examples of a polar bear and abrown bear, have the students make a chartof the differences between how the twobears live and survive in their environments.The chart should include the habitats of thebears, what kind of food they eat, how theircamouflage helps them survive in theirhabitat, and why each might not survivein the other’s environment.

• Developmental Delay • Learning Disability

Example of Natural SelectionThe lung disease tuberculosis (TB) is usually caused by the bac-terium Mycobacterium tuberculosis, shown in Figure 12, and it killsmore adults than any other infectious disease in the world. In the1950s, two effective antibiotics, isoniazid and rifampin, becameavailable, and they have saved millions of lives. In the late 1980s,however, new strains of M. tuberculosis that are largely or com-pletely resistant to isoniazid and rifampin appeared. Rates of TBinfection began to skyrocket in many countries, and in 1993 theWorld Health Organization declared a global TB health emergency.

How did antibiotic-resistant strains of M. tuberculosis evolve? Adetailed look at a single typical case reveals how: through naturalselection. This case is of a 35-year-old man living in Baltimore whowas treated with rifampin for an active TB infection. After 10 months,the antibiotics cleared up the infection. Two months later, however,the man was readmitted to the hospital with a severe TB infection,and despite rifampin treatment, he died 10 days later. The strain of M.tuberculosis isolated from his body was totally resistant to rifampin.

How had TB bacteria within his body become resistant torifampin? Doctors compared DNA of the rifampin-resistant bacteriato DNA from samples of normal, rifampin-sensitive M. tuberculosis.There seemed to be only one difference: a single base change fromcytosine to thymine in a gene called rpoB.

Evolution of Antibiotic Resistance Rifampin acts by binding to M. tuberculosis RNA polymerase,preventing transcription and so killing the bacterial cell. Themutation in the polymerase’s rpoB gene prevents rifampinfrom binding to the polymerase. The mutation, however, doesnot destroy the polymerase’s ability to transcribe mRNA. Themutation likely occurred in a single M. tuberculosis bacterialcell sometime during the first infection. Because its poly-merase function was no longer normal, the mutant bacteriumcould not divide as rapidly as normal bacteria can, but it stillcould divide. The antibiotic caused the normal bacterial cellsto eventually die. The mutant bacteria continued to grow andreproduce in the antibiotic-containing environment.

Because the total number of M. tuberculosis bacteria wasreduced drastically by the first antibiotic treatment, thepatient’s infection had seemed to clear. However, mutant,antibiotic-resistant bacteria survived and continued to growin his body. The mutant bacteria could reproduce moreeffectively in the presence of the antibiotic than the normalbacteria could. Therefore, the mutant bacteria became morecommon in the bacterial population, and they eventuallybecame the predominant type. When the patient becameacutely ill again with TB, the M. tuberculosis bacterial cellsin his lungs were the rifampin-resistant cells. In this way,natural selection led to the evolution of rifampin resistancein M. tuberculosis.

Figure 12 Tuberculosis.TB may be diagnosed from anX-ray of the lungs. TB iscaused by Mycobacteriumtuberculosis.

Mycobacterium tuberculosis

289

Using the FigureDirect students’ attention to Figure 13. Ask students to suggest a reason why beak size returns tonormal following each dry year. (Theenvironmental conditions that selectedfor large beak size were removed.) Askstudents what would have to happenfor beak size to remain large in thepopulation over many years. (Thearea would have to experience contin-ually dry weather.) Visual TAKS 3Bio 7A (grade 11 only), 7B

Group Activity Modeling Natural SelectionDivide students into small groupsand provide each group with one30-cm (1-ft) square of aluminumfoil and 10 each of 2.5-cm (1-in.)squares of aluminum foil and whitepaper. (Crinkle the foil and flattenit out before cutting the squares.)Have one student in each groupspread out the 20 small squares onthe larger square of aluminum.Give another student in each group10 seconds to pick up and removeas many squares as possible, one ata time, from the big sheet. Haveeach group count and report thenumber of aluminum squares andpaper squares “captured.” Keep atally on the board or overhead.More white paper squares than aluminum squares should be picked up. Thus, the camouflagedaluminum squares have an adaptivesurvival advantage. Ask: If the littlesquares could reproduce, whichtype would be more numerous inthe next generation? (small alu-minum squares) Why? (More ofthem were left to reproduce.)

Kinesthetic TAKS 3 Bio 7B; Bio 3ELS

LS

GENERAL



MISCONCEPTION ALERT

Many people think that selection pressureinduces changes. For example, people thinkthat antibiotics induce mutations in bacteriathat make them antiobiotic resistant. Remem-ber, natural selection does not induce changesin the genes of organisms; rather it selects forthose genes that are most adaptive. Genes forantibiotic resistance are already present inmany bacteria, but organisms expressingthese genes do not predominate until they aregrown in the presence of antibiotics and theresistance provides a survival advantage.TAKS 2 Bio 6C

Evolution in Darwin’s FinchesDarwin collected 31 specimens of finches from three islands whenhe visited the Galápagos Islands. In all, he collected 9 distinctspecies, all very similar to one another except for their bills. Twoground finches with large bills feed on seeds that they crush in theirbeaks, while two with narrower bills eat insects. One finch is a fruiteater, one picks insects out of cactuses, and yet another creeps upon sea birds and uses its sharp beak to drink their blood.

Darwin suggested that the nine species of Galápagos finches evolvedfrom an original ancestral species. Changes occurred as different pop-ulations accumulated adaptations to different food sources. This ideawas first tested in 1938 by the naturalist David Lack. He watched thebirds closely for five months and found little evidence to support Dar-win’s hypothesis. Stout-beaked finches and slender-beaked fincheswere feeding on the same sorts of seeds. A second, far more thoroughstudy was carried out over 25 years beginning in 1973 by Peter andRosemary Grant of Princeton University. The Grants’ study presents amuch clearer picture that supports Darwin’s interpretation.

It was Lack’s misfortune to study the birds during a wet year,when food was plentiful. The size of the beak of the finch is of lit-tle importance in such times. Slender and stout beaks both workwell to gather the small, soft seeds which were plentiful.

During dry years, however, plants produce few seeds, large orsmall. During these leaner years, few small, tender seeds were avail-able. The difference between survival and starvation is the ability toeat the larger, tougher seeds that most birds usually pass by. TheGrants measured the beaks of many birds every year. They found thatafter several dry years, the birds that had longer, more-massive beakshad better feeding success and produced more offspring.

When wet seasons returned, birds tended to have smaller beaksagain, as shown in Figure 13. The numbers of birds with differentbeak shapes are changed by natural selection in response to theavailable food supply, just as Darwin had suggested.

By relating the environment to beak size, the Grants showed thatnatural selection influences evolution.

Figure 13 Natural selection in finches

Beak-Size Variation

9.0

10.0

Dry year

Dry year

Wet year

Beak

size

(mm

)

Dry year

1977 1980 1982 1984

Year

Beak sizemeasured

290

Student Edition TAKS Obj 3 Bio 7B TEKS Bio 7B

Teacher Edition TAKS Obj 1 Bio/IPC 2C, 2D; IPC 3A TAKS Obj 2 Bio 6C TAKS Obj 3 Bio 7A, 7B TEKS Bio 3A, 3E, 6C, 7A, 7B;Bio/IPC 2C, 2D; IPC 3A

pp. 290–291

IPC Benchmark Fact

Have students compare and contrast the field obser-vations and subsequent conclusions reached by Lackversus the Grants. What was the principal weaknessof Lack’s scientific methodology? How did the Grantscorrect the flaw in Lack’s experimental procedure? Isit possible to improve the Grants’ scientific methodol-ogy? How? Ask students to explain why it is necessaryto conduct extended field observations or repeat labo-ratory experiments. TAKS 1 Bio/IPC 2A; IPC 3A; Bio 3A

Teaching TipSequential Diagram ofSpeciation Have students make aGraphic Organizer that shows eachstep of speciation in the propersequence. Have students use thefollowing terms: divergence, isola-tion, natural selection, new species,and variation. Bio 3E

GENERAL


Answers will vary. Sampleanswers might include thehypothesis that body form, especially the degree of left-rightsymmetry, correlates with geneticfitness. Studies have confirmedthat people find symmetry anattractive physical quality.

LogicalLS

Real Life

Use this graphic organizer withTeaching Tip on this page.

Graphic Organizer

Variation New speciesIsolationNatural

selection Divergence

Analyzing Changein LizardPopulationsSkills AcquiredInterpreting, analyzing,concluding, predicting

Teacher’s NotesPoint out to students that thegraph shown here is a scatterplot. The data points on such a graph are not connected bylines. Rather, these graphs illustrate the distribution andpatterns of the data.

Answers to Analysis1. The average hind limb length

of each population changed inresponse to differences in theaverage perch diameter ofplants on the different islands.

2. The population could evolveand have longer average hindlimbs, or it could go extinct.

3. The experiment illustrates thatcharacteristics of populationscan change over time inresponse to environmentalpressures. TAKS 1 Bio 2C, 2D

<x + 6x - 7 - 02

18

49376

0

52

Formation of New Species Species formation occurs in stages. Recall that natural selectionfavors changes that increase reproductive success. Therefore, aspecies molded by natural selection has an improved “fit” to itsenvironment. The accumulation of differences between groups iscalled (die VUHR jehns). Divergence leads to the for-mation of new species. Biologists call the process by which newspecies form (spee see AY shun).

Forming SubspeciesSeparate populations of a single species often live in several differ-ent kinds of environments. In each environment, natural selectionacts on the population. Natural selection results in the evolution ofoffspring that are better adapted to that environment. If their envi-ronments differ enough, separate populations of the same speciescan become very dissimilar. Over time, populations of the samespecies that differ genetically because of adaptations to differentliving conditions become what biologists call . The mem-bers of newly formed subspecies have taken the first step towardspeciation. Eventually, the subspecies may become so different thatthey can no longer interbreed successfully. Biologists then considerthem separate species.

Maintaining New SpeciesWhat keeps new species separate? Why are even closely relatedspecies usually unable to interbreed? Once subspecies becomedifferent enough, a barrier to reproduction, like the one shown inFigure 14, usually prevents different groups from breeding witheach other.

subspecies

speciation

divergence

Real LifeWhy do we find certainpeople pretty orhandsome? Some evolutionarybiologists think that manytraits that contribute to aperson’s attractivenessactually reveal the per-son’s fitness as a mate.Finding Information Research and comparehypotheses concerningbiological and culturalreasons that people judgeothers as attractive.

Figure 14 Mating activityin various frogs. Thoughthey appear to be similar, pick-erel frogs (Rana palustris) andleopard frogs (Rana pipiens)are different species. Thegraph shows that the time ofpeak mating activity variesbetween four species of frogs.

Leopard frog

Tree frog

Pickerel frog

Bullfrog

March 1 April 1 May 1 June 1 July 1

Mati

ng a

cti

vity

Month

Mating Activity in FrogsPickerel frog

Leopard frog

3A

291

ReteachingHave students suggest why sharksand alligators, which are consid-ered “living fossils,” have changedlittle over millions of years. (Theirenvironments, to which they are welladapted, have remained fairly con-stant over this time period.)

Quiz1. Divergence can lead to the for-

mation of new ________ and new________. (subspecies, species)

2. If two similar species of flower-ing plants bloom at differenttimes, what is the name of theprocess that keeps these speciesseparate? (reproductive isolation)

AlternativeAssessmentHave students make a labeleddiagram showing the process ofnatural selection using species oftheir choice. The chosen speciescould be one the student makes up.In their diagrams, students shouldinclude the four important pointsabout natural selection discussed inthis section. Bio 3E

GENERAL

GENERAL

CloseClose


1. (1) genetic variation, (2) environmental chal-lenges to reproduction, (3) overproduction ofoffspring and a struggle for survival and (4) anincrease in the number of individuals withcharacteristics suited to the environment

2. Bacteria have genetic variations that enablesome to survive and reproduce in the presenceof antibiotics. The non-resistant bacteria die,while the resistant bacteria reproduce.

3. The changes in the finches’ beaks were aresponse to changes in their food sources thatwere caused by climate changes.

4. As populations of a species spread throughoutan environment, they are exposed to varying

TAKS 3 Bio 7A (grade 11 only)

TAKS 3 Bio 7B

TAKS 3 Bio 7B

conditions (environmental pressures). Overtime, the separate populations become distinctand split into ecological races, and eventually,separate species.

5. It would take at least several generations andwould depend on how long it takes an organismto reach reproductive maturity.

6. A. Incorrect. The populations offinches were not isolated from one another. B.

Incorrect. There was no evidence of pollution. C.

Incorrect. Rain did not cause beak enlargement(though lack of rain, indirectly, was involved). D. Correct. Finch’s with larger beaks were able to eat the larger, tougher seeds. TAKS 3 Bio 7B

TAKS 3 Bio 7B

TAKS 3 Bio 7A (grade 11 only)


There are several types of barriers that may isolate two or moreclosely related groups. For example, groups may be geographicallyisolated or may reproduce at different times. Physical differencesmay also prevent mating, or they may not be attracted to one anotherfor mating. The hybrid offspring may not be fertile or suited to theenvironment of either parent.

Biologists have seen the stages of speciation in many differentorganisms. Thus, the way that natural selection leads to the formationof new species has been thoroughly documented. As changes continueto build up over time, living species may become very different fromtheir ancestors and from other species that evolved from the samerecent common ancestor, leading to the appearance of new species.

Analysis

1. Interpreting GraphicsHow did the average hind-limblength of each island’s lizardpopulation change from that ofthe original population?

2. Predict what would happento a population of lizards withshort hind limbs if they wereplaced on an island with alarger average perch diameterthan from where they came.

3. Justify the argument that this experiment supports thetheory of evolution by naturalselection.

Analyzing Change inLizard PopulationsBackground

In 1991, Jonathan Losos, an American sci-entist, measured hind-limb length of lizardsfrom several islands and the average perchdiameter of the island plants. The lizardswere descended from a common popula-tion 20 years earlier, and the islands haddifferent kinds of plants on which thelizards perched. Examine the graph at rightand answer the following questions:

<x + 6x - 7 - 02

8

493 0

52

Incre

asi

ng

perc

h d

iam

ete

r

Increasing hind-limb length

Each island's lizard population

Original lizard population

Hind-Limb Length Variation

List four elements of natural selection. 7B

Describe the mechanism that causespopulation changes in antibiotic-resistant bacteria. 7B

Identify what caused the change in the finch’sbeaks as seen in the Grants’ study. 7A

Describe how speciation takes place. 7A

Critical Thinking Evaluating Results Basedon the results of David Lack’s study and theGrants’ study of finches, what conclusion canyou make about the length of time required forevolution of a new species to take place?

The beaks of finches on theGalápagos Islands enlarged over generations inresponse to 7B

A isolation. C rain.B pollution. D limited food supply.


Section 3 Review

2C 2D 7A

www.scilinks.orgTopic: Species FormationKeyword: HX4167

3F 7B

292

Student Edition TAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B TEKS Bio 3F, 7A, 7B

Teacher’s Edition TEKS Bio 3E

pp. 292–293

AlternativeAssessmentHave students list the key termsused in this chapter and a brief def-inition of each term. Have themconstruct crossword puzzles usingthe definitions as the clues.

GENERAL


• Science Skills Worksheet• Critical Thinking Worksheet• Test Prep Pretest• Chapter Test GENERAL

GENERAL

GENERAL


Answer to Concept Map

The following is one possible answer to Performance Zone item 15 on the next page.

is driven by

which requires

which lead to

which results in

Evolution

natural selection

extinction

genetic variationpopulation

divergence

speciation

environment

occurs in

does not occur ifspecies cannot adapt

conditionsin the

which can result in

Key Concepts

Study CHAPTER HIGHLIGHTS

ZONEKey Terms

Section 1population (278)natural selection (279)adaptation (279)reproductive isolation (281)gradualism (282)punctuated equilibrium (282)

Section 2paleontologist (285)vestigial structure (286)homologous structure (286)

Section 3divergence (291)speciation (291)subspecies (291)

The Theory of Evolution by Natural Selection

● Charles Darwin concluded that animals on the coast of SouthAmerica that resembled those on the nearby islands evolveddifferences after separating from a common ancestor.

● Darwin was influenced by Thomas Malthus, who wrote thatpopulations tend to grow as much as the environment allows.

● Darwin proposed that natural selection favors individualsthat are best able to survive and reproduce.

● Under certain conditions, change within a species can leadto new species.

● Gradualism is a process of evolution in which speciationoccurs gradually, and punctuated equilibrium is a processin which speciation occurs rapidly between periods of littleor no change.

Evidence of Evolution

● Evidence of orderly change can be seen when fossils arearranged according to their age.

● Differences in amino acid sequences and DNA sequencesare greater between species that are more distantly relatedthan between species that are more closely related.

● The presence of homologous structures and vestigial struc-tures in vertebrates suggests that all vertebrates share acommon ancestor.

Examples of Evolution

● Individuals that have traits that enable them to survive in agiven environment can reproduce and pass those traits totheir offspring.

● Experiments show that evolution through natural selectionhas occurred within populations of antibiotic-resistantbacteria and in Darwin’s finches.

● Speciation begins as a population adapts to its environment. ● Reproductive isolation keeps newly forming species from

breeding with one another.

3

2

1

293

IPC BenchmarkReview

To prepare students for the TAKS, havestudents review Waves: Types of Wavesin Real Systems and ElectromagneticWaves TAKS Obj 5 IPC 5A on pp. 1059–1061 of the IPC Refresher inthe Texas Assessment Appendix of thisbook.

ANSWERS

Using Key Terms

1. b TAKS 3 Bio 7B2. b TAKS 3 Bio 7A (grade 11 only)3. d TAKS 3 Bio 7B4. a TAKS 3 Bio 7B5. a. An adaptation is a trait that

enables an organism to better sur-vive in its environment; naturalselection is the process by whichpopulations change in response totheir environment. b. Extinctionrefers to the death of all membersof a species; isolation refers to theseparation of populations of thesame species and their resultinginability to interbreed. c. Popu-lations are groups of individualsof the same species living in the same area; subspecies arepopulations of the same speciesthat differ genetically because ofadaptations to different condi-tions. d. The word homologousrefers to structures that share acommon ancestry. The word ves-tigial refers to structures that arereduced in size and have no func-tion or a less important functionthan they do in other, relatedorganisms. e. Divergence is theaccumulation of differencesbetween groups; speciation is theprocess by which species form.

Understanding Key Ideas

6. b TAKS 3 Bio 7B7. b TAKS 3 Bio 7B8. a TAKS 3 Bio 7B9. It may indicate that these animals

share a common ancestor. TAKS 3Bio 7B

10. No; there is no genetic variation upon whichnatural selection can operate. TAKS 3 Bio 7B

11. The greater the number of nucleotide differ-ences between two species, the more distant istheir most recent common ancestor. TAKS 2Bio 6A; TAKS 3 Bio 7B

12. Subspecies are populations of the samespecies that differ genetically because of adap-tation. This is the first step toward speciation.TAKS 3 Bio 7A

13. Meiosis is beneficial to the evolution of aspecies because it provides a source of geneticvariation upon which natural selection can act.

14. erosion or other destructive geologicalprocesses TAKS 3 Bio 7A (grade 11 only)

15. The answer to the concept map is found atthe bottom of the Study Zone page. TAKS 1Bio/IPC 2C

Section Questions1 1, 2, 6, 8, 13, 14, 16, 17, 19, 20, 212 7, 9, 11, 18, 223 3, 4, 5, 10, 12, 15, 18, 22

Assignment Guide


CHAPTER 13

Using Key Terms1. The process by which a species becomes

better adapted to its environment is calleda. gradualism.b. adaptation.c. natural selection.d. reproductive isolation.

2. Anatomical structures that share a commonancestry are called _______ structures.a. vestigial c. analogous b. homologous d. evolutionary

3. In Lack’s study, the effect of weather on thesize of the finch’s beak is an example of a. speciation. b. reproductive isolation. c. fossilization. d. natural selection.

4. The process by which isolated populationsof the same species become new species iscalleda. speciation. b. reproductive isolation. c. genetic variation. d. natural selection.

5. For each pair of terms, explain thedifferences in their meanings.a. adaptation, natural selectionb. extinction, reproductive isolationc. population, subspeciesd. homologous, vestigiale. divergence, speciation

Understanding Key Ideas6. According to the modern theory of evolution,

a. Lamarck was completely wrong.b. random gene mutation is a part

of evolution.c. punctuated equilibrium has replaced

natural selection.d. the diversity of life-forms resulted

from the inheritance of acquiredcharacteristics.

7. With respect to the problem of antibiotic-resistant tuberculosis, which entity evolves?a. the patientb. the bacteriumc. the antibioticd. None of the above.

8. What is true about gradualism with respectto punctuated equilibrium?a. Each is a model of evolution.b. Neither is a model of evolution.c. Only gradualism portrays true evolution. d. Only punctuated equilibrium portrays

true evolution.

9. Adult lobsters and barnacles look verydifferent. The larvae of barnacles andlobsters, however, are practically identical.What does this indicate about the evolu-tionary history of these organisms?

10. Could a population of identical organismsundergo natural selection? Why or why not?

11. Explain the relationship between thenumber of nucleotide differences betweentwo species and the time since the speciesshared a common ancestor.

12. What is a subspecies, and how is forma-tion of a subspecies related to the processof speciation?

13. How is meiosis beneficial to the evolutionof a species by natural selection? (Hint:See Chapter 7, Section 1.)

14. Other than punctuatedequilibrium, what naturally occurringphenomena might explain large gaps in the fossil record?

15. Concept Mapping Make a conceptmap that shows how natural selection leadsto speciation. Try to include the followingterms in your map: evolution, naturalselection, genetic variation, environment,speciation, and divergence.

PerformanceZONE

CHAPTER REVIEW

7B

7B

7B

7B

7B

7B

7A

7A

2C 3C

6A 7B 9A

7B

7B

7A

294

Review and AssessTAKS Obj 1 Bio/IPC 2C, 2DTAKS Obj 1 IPC 3ATAKS Obj 2 Bio 6ATAKS Obj 3 Bio 7A, 7BTEKS Bio 3A, 3D, 6A, 7A, 7B; Bio/IPC 2C, 2D; IPC 3A

Critical Thinking

16. No, natural selection can onlyoperate on traits that affectreproductive success.

17. The relationship is so importantbecause the pace and nature bywhich populations change overtime, or evolve, is largely drivenby natural selection. TAKS 1 IPC 3A;Bio 3A

18. Genetics reveals how traits arepassed from one generation toanother. This understanding sup-ports Darwin’s theory by explain-ing how offspring can havecharacteristics found in their par-ents, whether or not such charac-teristics are expressed. Geneticsalso supports Darwin’s theory byproviding tools for measuringhow closely organisms are relatedto one another.

19. The shorter the generation time is for an organism, the faster the rate of evolution will be forthat organism. This is becausenatural selection will have moregenerations to act upon in a giventime period.

Alternative Assessment

20. Answers will vary. Bio 8B21. Answers will vary. Students

should note that Wallace collectedinsects on an 1848 expedition tothe Amazon. He also made obser-vations in the Malay Archipelagobetween 1854 and 1862. Wallacediscovered that animals on thewestern islands of the Malayarchipelago differed sharply fromthose on the eastern islands.

22. Paleontologists are scientists whostudy fossils and other remains ofpast life. They are concerned withall aspects of ancient life, includingthe environments that existed atthe time. Paleontologists usuallyhave at least an undergraduatedegree in zoology and/or geology,including training in chemistry andphysics. University and museumjobs usually require a Ph.D. Mostpaleontologists are employed byuniversities, museums, or large oiland construction companies.Growth potential for this field isfair. Starting salary will vary byregion. Bio 3D

TAKS 1 Bio/IPC 2D

TAKS 3 Bio 7B

TAKS 3 Bio 7B

TAKS 3 Bio 7B

Standardized Test Prep 1. A. Incorrect. Warbler finches and armadillos

are distantly related. B. Incorrect. Warblerfinches and armadillos do not share a recentcommon ancestor. C. Correct. Warbler finchesand armadillos share a remote commonancestor (early vertebrate). D. Incorrect. Bothwarbler finches and armadillos evolved fromolder forms of life.

2. F. Incorrect. See answer J. G. Incorrect. Seeanswer J. H. Incorrect. The glyptodont and anearly vertebrate are more distantly related than

TAKS 3 Bio 7B

the glyptodont and the armadillo, so their DNA isnot the most similar. J. Correct. The glyptodontand armadillo diverged most recently from oneanother, so their DNA is most similar. TAKS 3Bio 7A (grade 11 only)

3. A. Correct. By definition, different species cannot interbreed. B. Incorrect. Different speciesmight have homologous structures. C. Incorrect.Different species might or might not have verydifferent embryos. D. Incorrect. The woodpeckerfinch and the warbler finch are more similar toeach other than they are to glyptodonts. TAKS 3Bio 7B


Use the diagram below and your knowledge ofscience to answer questions 1–3.

1. The diagram implies that warbler finchesand armadillos A are unrelated.B share a recent common ancestor.C share a remote common ancestor. D did not evolve from older forms of life.

2. Which organism has DNA that is probablymost similar to the glyptodont’s DNA? F woodpecker finch H early vertebrateG warbler finch J armadillo

3. Because the woodpecker finch and thewarbler finch are different species, theyprobably A cannot interbreed. B lack homologous structures.C develop from very different embryos.D are more similar to glyptodonts than to

each other.

Test

Critical Thinking16. Applying Information If a favorable trait

increases the life span of an organismwithout affecting reproductive success,does evolution occur?

17. Evaluating Analyze Darwin’s theory of evo-lution by natural selection and describeone strength and one weakness.

18. Justifying Conclusions About 40 years afterthe publication of On the Origin of Species,genetics was recognized as a science. Ex-plain how information about genetics mightsupport Darwin’s theory of evolution.

19. Applying Information What effect would thetime from the beginning of an organism’slife to the point of reproduction have on therate of evolution of a species, and why?

Alternative Assessment20. Being a Team Member With two to three

other students, locate and examine photo-graphs and drawings of the tortoises thatDarwin observed on the Galápagos Islands.Plan and produce a mural showing the tor-toises in their natural environment.

21. Communicating Prepare an oral report onthe biological research of Alfred Russel Wallace. Present your findings to your class.

22. Career Connection Paleontologist Researchthe field of paleontology, and write a reporton your findings. Your report shouldinclude a job description, trainingrequired, kinds of employers, growthprospects, and starting salary.


Woodpeckerfinch

Warblerfinch

Glyptodont

Armadillo

Recent commonancestor

(armadillo-likemammal)

Recent commonancestor

(finch-like bird)

Remote commonancestor

(early vertebrate)Do not be fooled by answers that may seemcorrect to you because they contain unfamiliarwords.

7B

3A

7B

7B

8B

3D

2D 3F

7B

7A

7B

295

Documents

Section 1 The Theory of Evolution Focus by Natural · PDF file · 2011-08-18Darwin’s theory of evolution by ... Section 1 276 Chapter 13 • The Theory of Evolution Pg. 276: 3A,